1. Field of the Invention
This invention relates to a device for automatically raising and lowering adjustable mobile elements of chairs and beds and is intended particularly, in the case of chairs and beds for invalids, to permit the operation by the invalids of these adjustable elements without requiring special effort on their part.
2. The Prior Art
Devices are already known, driven by motor or hydraulically, to modify the inclination of the backs, bed surfaces and support surfaces of chairs and beds. Now, motor-driven devices are expensive in design and are used only with special chairs and beds. Adjustment devices operating hydraulically are also extremely expensive.
FR No. 1 542 464 has proposed a device making it possible to raise and lower adjustable elements of chairs and beds, which uses a pneumatic spring that is continuously adjustable and actuated by a handle.
The user of a pneumatic spring is actually at an advantage because such a spring, because of its particular structure, is always able to keep the element to be adjusted approximately in balance. For this reason, it suffices, after unlocking of the cylinder by the person on the bed or chair, to exert a relatively slight force to cause a break in the balance and to allow the movement of the element to be regulated in the desired direction. Further, a pneumatic spring is much less expensive than the motors or hydraulic systems used up to now.
However, in the device of this FR No. 1 542 464, the person, seated on the chair or lying in the bed, must exert a rather considerable force at the level of the abdominal muscles particularly to lower or raise the mobile element. The device therefore cannot be used by very weak persons confined to bed or having only slight abdominal musculation.
Further, this FR No. 1 542 464 shows only an embodiment for swinging the back of a bed and shows a very complicated system for controlling the pneumatic cylinder.